1. Field of the Invention
The present invention relates to a drain pump of a forced drain type automatic washing machine, and more particularly, to an apparatus for reducing noise and vibration of a drain pump which is capable of reducing noise and vibration that are generated in the initial driving of the drain pump.
2. Description of the Background Art
In order to wash dirty clothes, they are put in a washing fluid mixed with a detergent, so that the dirt is separated from the clothes owing to a chemical action of the detergent. But only using the action of the detergent makes the washing to take a long time. Thus, a washing machine is employed to speed the washing, by which a mechanical action such as friction or vibration is applied to the clothes, to speed the separation of the dirt from the clothes.
Washing operation of the washing machine is controlled as follows.
First, a washing phase is performed in a manner that after sensing the amount of laundry of the clothes in a washing tub for judgement, the amount of wash water and the detergent, a kind of flow and an overall washing time are set. And then, the water is eddied by the forward and backward rotation of a pulsator, which causes a friction over the laundry, thereby separating the dirt from the laundry.
As the washing phase is completed, a rinsing phase is performed in a manner that the muddy water in the washing tub is discharged and fresh water is supplied to the washing tub for rinsing the laundry as pre-set by the system.
After the rinsing phase, a dehydrating stroke is performed in a manner that the water in the washing tub is discharged, and an induction motor is rotated at a predetermined high speed to water off the laundry by a centrifugal method.
As mentioned above, when the laundry in the washing tub is washed with the washing operation controlling performed, a drain pump is used to forcibly drain the water.
A general drain pump of a conventional art is shown in FIGS. 1 to 3B, of which the outer appearance is formed by a rotor chamber 11 and an impeller chamber 12 coupled to the rotor chamber 11.
The impeller chamber 12 includes an inlet 13 and an outlet 14, paths through which the water flows in and out by pumping action at its upper and side surfaces.
A magnet housing 17a is formed at one side of the rotor chamber 11, and one side of a stator 15, forming a magnetic field as power is applied thereto, and is combined to the circumferential surface of the magnet housing 17a. 
The other side of the stator 15 is extended in the axial direction, and a bobbin 16 is combined on the outer surface thereof. A coil C is wound on the bobbin 16.
As shown in FIG. 2, a magnet 17 is inserted in the magnet housing 17a, and a rotational shaft 18 is axially formed integrally at the central portion of the magnet 17, and as shown in FIG. 3A, a shaft tap 18a is protrusively formed at the upper end portion of the rotational shaft 18.
An impeller 19 is combined to the shaft tap 18a. In detail, a tap receiving portion S1 is formed inside the central portion of the impeller 19 to receive the shaft tap 18a, and an impeller tap 19a is formed at one side of the tap receiving portion S1 to prevent the magnet 17 from rotary-idling by contacting with the shaft tap 18a. 
Meanwhile, as shown in FIGS. 3A and 3B, in order to prevent the impeller 19 from separating from the rotational shaft 18, a circular fixing disk 20 is fixed in the inner circumferential surface of the impeller 19 as being combined to the rotational shaft 18 at the lower portion of the shaft tap 18a. 
With the conventional drain pump constructed as described above, when power is applied to the stator 15 and thus a magnetic field is generated, the rotational shaft 18 integrally formed with the magnet 17 is rotated according to the mutual interaction of the stator 15 and the magnet 17.
Thus, as the rotational shaft 18 is rotated, the impeller 19 combined to the rotational shaft 18 is accordingly rotated, thereby performing the pumping action for draining.
In this respect, the initial driving of the pump needs to generate a torque strong enough to overcome the magnetic force for performing the pumping action, because the stator 15 made of magnetic material and the magnet 17 are attracted to each other due to the magnetic force just before the initial driving of the pump.
The initial driving of the pump will now be described in detail. As shown in FIG. 3B, the initial driving of the pump is controlled as the shaft tap 18a protrusively formed at the upper end portion of the rotational shaft 18 that is integrally formed to the magnet 17 contacts with the impeller tap 19a formed in the tap receiving portion S1 so as to be coupled to the shaft tap 18a. 
That is, at the same time when power is supplied, only the rotational shaft 18 is idly rotated at maximum 270xc2x0 depending on relative instantaneous positions of the shaft tap 18a and the impeller tap 19a, and when the shaft tap 18a and the impeller tap 19a contact with each other, the rotational shaft 18 and the impeller 19 are integrally rotated, thereby performing the pumping action.
In this respect, in order to prevent a noise generated when the impeller tap 19a and the shaft tap 18a contact with each other, a grease is inserted into the tap receiving portion S1, by which the tap receiving portion S1 is sealed with O-ring 21.
However, the conventional drain pump as described above has disadvantages in that since the tap is not able to be directly formed on the rotational shaft, an additional means is necessary to insert the shaft tap and the O-ring, for which a process and an equipment are additionally required to forcibly fix the shaft tap and the O-ring to the rotational shaft.
Also, since the shaft tap may be easily broken when it contacts with the impeller tap, the tap is to be made by brass material, causing a difficulty in process for fabricating the tap formation and increase in expense.
Moreover, in case that hot water is pumped by the drain pump, since the impeller makes a heat distortion, the impeller tap is deformed, resulting in that it is not coupled to the shaft tap properly.
Most of all, even though the shaft tap and the impeller tap are sealed by the O-ring to prevent a noise caused when they contact with each other, coupling noise and vibration are still generated, causing users inconvenience.
Therefore, an object of the present invention is to provide an apparatus for reducing noise and vibration of a drain pump in which a buffer is provided to buffer an impact caused when an impeller tap and a coupling tap are coupled each other, so that parts can be prevented from breaking down in the initial driving of a drain pump, noise and vibration can be minimized, and a pumping performance can be improved.
Another object of the present invention is to provide an apparatus for reducing noise and vibration of a drain pump in which a magnetic material is combined to a magnet, thereby simplifying the form of the coupling portion of a rotational shaft and an impeller.
To achieve these and other advantages and in accordance with the purposed of the present invention, as embodied and broadly described herein, there is provided an apparatus for reducing noise and vibration of a drain pump including: a rotor rotated by a mutual interaction with a stator; a rotational shaft rotated by being directly combined to the rotor; a coupling cylinder combined to an end portion of the rotational shaft; a coupling tap protrusively formed on an outer circumferential portion of the coupling cylinder; an impeller including a receiving portion in which the coupling cylinder is received and rotated by receiving a rotation force from the rotational shaft; an impeller tap protrusively formed on an inner circumferential portion of the receiving portion in the impeller and positioned at a predetermined part of a rotation trajectory of the coupling tap to contact with the coupling tap; and a buffer member of a ring shape with a gap therein located on a rotational path of the coupling tap to move along with the coupling tap in order to buffer between the coupling tap and the impeller tap when the two taps contact to each other.
In order to achieve the above object, there is also provided an apparatus for reducing noise and vibration of a drain pump including: a rotational shaft of a driving source; an impeller rotated by receiving a rotation force from the rotational shaft; a coupling tap and an impeller tap formed on the rotational shaft and on the impeller, respectively, for transmitting the rotation force by contacting and coupling to each other after the rotational shaft idly rotates through a predetermined angle; and a buffering magnetic means for absorbing, by a mutually repulsive force, shock generated when the coupling tap and the impeller tap contact to each other using a repulsive force.